This invention relates generally to a transfer film, and more specifically to a unique transfer film for holographic images. More particularly, this invention relates a transfer film designed to receive a holographic image that is imparted to a subsequently applied metallized layer, and then permits the metallized layer with the holographic image therein to be transferred onto another substrate, to thereby provide the holographic image on that other substrate.
The art of transferring a holographic image from one substrate to another is known, as is exemplified in U.S. Pat. Nos. 5,662,986; 5,735,989; 5,723,203; 5,746,865; 5,766,734; 5,871,608; 5,900,095 and 5,902,436. The subject matter of all of the aforementioned patents is incorporated herein by reference. All of the above-identified patents describe processes for transferring a holographic image from a transfer film to another substrate, but only generally disclose polymeric transfer films. In fact, all of the above-identified patents state that the transfer films xe2x80x9cinclude many of the commonly available plastics, for example. These will include polyethylenes, polypropylenes, polyethylene terephthalates, among others, for example. These substrates are usually 0.5 to 4.0 mils in thickness.xe2x80x9d
It is known in the prior art to form multilayer polyolefin films including a central core and one or more outer functional layers, with one of said layers being a propylene/ethylene copolymer heat seal layer. These films have been determined to be unsatisfactory for use in achieving multiple transfers of embossed metallized layers from the multilayer film to another substrate.
Although it also is known in the prior art to include additives, such as glycerol monostearate (GMS) and ethoxylated stearylamine in polyolefin films to provide a smooth surfaced, or non-holographic release film, this technology has not been employed or utilized in connection with any transfer films employed to achieve one or more transfers of a holographic image to another substrate.
Accordingly, a need exists for an improved transfer film for holographic images, which permits multiple transfers of the image to another substrate without unacceptable degradation of the holographic image. It is to such an improved transfer film that the present invention relates.
It is a general object of this invention to provide a transfer film for holographic images that is reliable in use.
It is a further object of this invention to provide a transfer film for holographic images that permits multiple transfers to be achieved in a reliable manner.
It is a further object of this invention to provide a transfer film for holographic images that permits multiple transfers of the image to another substrate, such as a thin tissue paper substrate, a foil substrate, a board stock or other desired substrate.
It is a more specific object of this invention to provide a transfer film that permits the multiple transfer of holographic images to a packaging substrate, such as a substrate employed to package food products.
It is a further object of this invention to provide a holographic transfer film for use in transferring a holographic image to a substrate of the type that generally is not capable of directly receiving a holographic image impressed into it, e.g., thin tissue paper, which is too flimsy and thin to directly receive a holographic image impressed directly into it.
It is a further object of this invention to provide a transfer film for holographic images that can be employed to transfer the holographic image to a substrate in a manner that does not undesirably modify the properties of the substrate.
The above and other objects of this invention are achieved in a transfer film for holographic images wherein the film is a multilayer structure including a core and at least one outer layer having a sufficient thickness for receiving a holographic image impressed into it. The outer layer for receiving the holographic image is thinner than the core layer and is a propylene/ethylene random copolymer having a DSC melting point in excess of 120xc2x0 C. and less than 140xc2x0 C. The outer layer further includes an antistatic/release additive in it for permitting multiple releases of a metallized layer that initially is applied to the outer layer of the transfer film having the holographic image impressed into it, onto a surface of another substrate.
In a preferred embodiment of this invention both the core and the outer layer for receiving the holographic image include an antistatic/release additive.
In a preferred embodiment of this invention the core is a polypropylene homopolymer.
In a preferred embodiment of this invention the outer layer is at least as thick as the depth of the holographic image impressed into it; most preferably in the range of 4-8 gauge.
In a preferred embodiment of this invention the outer layer has a thickness in excess of 6 gauge, and more preferably approximately 6.5 gauge.
In a preferred embodiment of this invention the release additive, which is in either the outer layer, or in both the outer layer and the core layer includes glycerol monostearate and ethoxylated stearylamine.
In a preferred embodiment of this invention the DSC melting point of the outer layer is in the range of 130xc2x0 C. to 140xc2x0 C., and more preferably approximately 134xc2x0 C.
In certain embodiments of this invention, the transfer film is a multilayer structure including a core and opposed outer layers on opposite sides of the core. In these embodiments, one outer layer for receiving a holographic image impressed into it is thinner than the core layer and is a propylene/ethylene random copolymer having a DSC melting point in excess of 120xc2x0 C. and less than 140xc2x0 C., said one outer layer further including a release additive therein for permitting multiple releases of a metallized layer that initially is applied to the one outer layer of the transfer film having the holographic image impressed into it, onto a surface of another substrate.
In the preferred embodiments of this invention wherein the multilayer structure includes opposed outer layers, the outer layer opposed to the outer layer that receives the holographic image therein includes a slip agent in it.
Most preferably, when the multilayer structure includes opposed outer layers, the outer layer opposed to the one that receives the holographic image therein is treated to provide improved ink-receptivity and/or lamination properties; most preferably by either corona-treating or flame-treating that surface.